Niemann hasn't pitched since May 14 when he left a start at Toronto with a fractured right leg after being struck by Adam Lind's line drive. Niemann was 2-3 with a 3.88 ERA in seven starts before the injury.
The Rays will call up four players from Triple-A Durham when rosters expand Saturday. Joining the team will be infielder Reid Brignac, catcher Chris Gimenez, left-hander Cesar Ramos and outfielder Rich Thompson.
The Rays also recalled infielder Sean Rodriguez and placed him on the 15-day DL. Rodriguez broke his right hand while punching a locker at Triple-A Durham.